1. Field of the Invention
The present invention relates to a laminated capacitor.
2. Description of the Related Art
Laminated capacitors of small size such as 1608 (1.6 mm×0.8 mm), 1005 (1.0 mm×0.5 mm) and 0603 (0.6 mm×0.3 mm) are inferior to large laminated capacitors in terms of bending strength, and therefore more vulnerable to cracks and breaking due to forces applied to the capacitor body when the capacitor body is installed on a circuit board, after it has been mounted, and in other situations. Here, “bending strength” represents the value measured in a test method conducted by supporting the external electrodes of the laminated capacitor and pushing the lengthwise center of the laminated capacitor using a pressure jig, where, specifically, the load that causes the capacitor to break is indicated in gf, N, Pa or other units.
To improve the bending strength of a small laminated capacitor, a reinforcement layer can be provided inside the capacitor body. There are two approaches regarding how to provide this reinforcement layer. One is to add a metal layer, which is different from an internal electrode layer, as a reinforcement layer, while the other is to use an internal electrode layer as a reinforcement layer.
It should be noted that structures that can be utilized according to the former approach are disclosed in Patent Literatures 2 and 3 as mentioned below, while structures that can be utilized according to the latter approach are disclosed in Patent Literatures 1, 4 and 5 as mentioned below, although these structures are not intended to improve the bending strength.
The structures disclosed in Patent Literatures 2 and 3 have a metal layer added to the top and bottom margins (where there is no internal electrode layer) of a capacitor body. Since the added metal layers are not connected to external electrodes, the bending strength does not improve much.
The structure disclosed in Patent Literature 4 has two adjacent internal electrode layers in a capacitor body connected to the same external electrode. This structure can improve the bending strength more than can the structures disclosed in Patent Literatures 2 and 3, but because the two internal electrode layers are provided only on one external electrode side, the mechanical strength of the other external electrode side of the capacitor body becomes lower than the mechanical strength on the one external electrode side. Also, the thickness of the dielectric layer present between the two internal electrode layers connected to the same external electrode is equal to or greater than the thickness of the dielectric layer present between the two internal electrode layers connected to different external electrodes, which increases the height dimension of the laminated capacitor or decreases the number of internal conductive layers contributing to the formation of capacity if the aforementioned increase in height dimension is to be avoided, and the overall capacity of the laminated capacitor will drop.
The structures disclosed in Patent Literatures 1 and 5 have an additional internal electrode layer connected to one external electrode in such a way as to face the top internal electrode layer among the internal electrode layers connected to the one external electrode, as well as an additional internal electrode layer connected to the other external electrode in such a way as to face the bottom internal electrode layer among the internal electrode layers connected to the other external electrode. These structures can improve the bending strength more than can the structure disclosed in Patent Literature 4, but because the thicknesses of the dielectric layers (dielectric layers not contributing to the formation of capacity) each present between the additional internal electrode layer and the internal electrode layer facing the additional internal electrode layer are the same as the thickness of the dielectric layer (dielectric layer contributing to the formation of capacity) present between the two internal electrode layers connected to the different external electrodes, the height dimension of the laminated capacitor increases or the number of internal conductive layers contributing to the formation of capacity decreases if the aforementioned increase in height dimension is to be avoided, and the overall capacity of the laminated capacitor will drop.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.